In the field of satellites, isolation between the satellite and the launcher assumes a major significance. Thus, in order to avoid transmission of the vibration generated by the launcher to the structure of the satellite and thereby to the equipment carried by the satellite, it is known to place isolation means between the satellite and the launcher. The isolation means must be capable of being effective over a wide frequency range and have sufficient mechanical performance to ensure the fastening and good mechanical strength of the satellite on the launcher.
More specifically, the launcher comprises a satellite interface ring and the satellite comprises a launcher interface ring. The interface rings are connected together by isolation means, for example isolation modules. By the term “isolation” is meant at least a reduction in the amplitude of the vibration through the module between on the one hand the source of vibration, i.e. the device generating vibration, and on the other hand, the structure to be isolated. Thus in certain cases, the isolation module must also enable impacts to be attenuated.
It is known to use isolation means including elements made from viscoelastic material.
However, a problem frequently encountered is the nonlinear behaviour of the isolation means, due in particular to the viscoelastic nature of the material used. Now, the nonlinearity limits the ability to predict the behaviour of the isolation means. Thus, changes in the size, weight and geometry of the launcher and of the satellite make it necessary to revisit the design of the isolation means, which must be developed on a case-by-case basis. Moreover, unexpected events generating vibrations and impacts during the satellite launch phase may have negative effects on the control of the launcher and of the satellite, due in part to the unpredictable behaviour of the isolation means.
As a result, the use of elements made from viscoelastic material in the particular field of satellites is limited.
Novel designs have therefore been proposed for isolation means, reducing the nonlinear behaviour so as to obtain isolation means that are effective for different types of launchers and satellites, the behaviour of which is predictable.
Document U.S. Pat. No. 6,199,801 describes an example of an isolation device in the form of a module. A plurality of modules is placed between the launcher and the satellite in order to ensure their connection. A module behaves like a spring in a vertical direction, but is relatively rigid in the lateral directions. For example, a module is in the form of two metal beams, a shock-absorbent layer made from viscoelastic material being applied to each beam. The two beams are connected together by vertical metal portions. Thus, by making the loads pass through the very stiff vertical metal portions, the modules would gain in linearity. The layers of viscoelastic material have an auxiliary role and are only stressed in order to absorb vibrations in the event of significant deflection of the beams.
However, such a module is found to be very stiff in the lateral directions, making it inadequate to ensure lateral isolation.
Document U.S. Pat. No. 7,249,756 also relates to the problems of nonlinearity of the isolation modules. It proposes to make an isolation module effective in all directions. To this end, the module comprises a central flexure portion and two flexure loops, symmetrical with respect to the central portion. On each face of each loop, a layer of a viscoelastic material and a rigid metal layer are applied successively. The central portion in fact comprises two superimposed sections that can move in relation to each other both longitudinally and laterally. These movements are reflected in the loops, more specifically in the layers of viscoelastic material, which deform under shear due to the rigid layers.
The use of metal parts makes it possible to reduce the problems associated with nonlinear behaviour. However, as before, the lateral flexibility is very low, in any case too low to supply adequate lateral isolation.
Moreover, such a module constituted by a stack of layers proves to be a complex structure. Costs are thereby increased. Moreover, such a structure is bulky and heavy, which is highly undesirable in the field of satellites, where bulk and weight must be minimal. In addition, the use of metal layers necessarily involves the use of layers made from viscoelastic material in order to provide damping, necessarily introducing nonlinearity.
There is a need for a novel isolation module providing in particular a solution to the aforementioned drawbacks.